Convection
When you boil water in the kettle, even if you heat only the bottom, the whole water becomes evenly hot. This is because water transfers heat while moving directly. In this way, liquid or gaseous substances can transfer heat while moving directly elsewhere. This phenomenon is called convection.
Examples of convection you can see around us
When you turn on the radiator installed at the bottom, the warmed air rises up, and the surrounding cold air comes down to the radiator and warms up. This convection causes the entire room to warm evenly over time.
Conversely, when you turn on an air conditioner installed in a high place, the upper air cools down and moves downwards, while the lower air moves upwards to cool the entire room evenly.